Heat exchangers are used to transfer heat from one fluid to another fluid. Heat exchangers have various uses within an automotive vehicle. For example, in a radiator, heat is transferred from a cooling liquid to the ambient air. In particular in motor vehicles the heat exchanger is used to discharge waste heat released by the internal combustion engine into the ambient air. The cooling medium that flows through the heat exchanger may be a liquid or, in some applications, a gaseous fluid.
Heat exchangers of the radiator type include a plurality of parallel tubes and two header boxes. The header boxes are typically multi-part structures having a header tank and a tube header. The tube header includes a central header plate with passages bordered by side walls forming a ferrule. The ends of the tubes are inserted into the ferrules to establish a fluid communication between the tube header and the interior volume of the tubes. The tubes may be formed from folded or welded sheet metal. While welded tubes are generally more durable, folded tubes are less costly to manufacture.
During operation, the service life of the heat exchanger may be shortened due to non-uniform expansion of the individual components of the heat exchanger when heating up and cooling down and the deformation or displacement resulting therefrom. The stresses can be attributed to the changing thermal conditions in the heat exchanger. The service life of a heat exchanger may thus be shorter for heat exchangers with folded tubes than for those with welded tubes.
In the past, attempts have been made to extend the service life of heat exchangers by modifying the transition between the tube header and the inserted folded tubes, with limited success.